Solid state lights (“SSLs”) use solid state emitters (“SSEs”) as sources of illumination. Generally, SSLs generate less heat, provide greater resistance to shock and vibration, and have longer life spans than conventional lighting devices that use filaments, plasma, or gas as sources of illumination (e.g., florescent or incandescent lights).
A conventional type of SSL is a “white light” SSE. White light requires a mixture of wavelengths to be perceived as white by human eyes. However, SSEs typically only emit light at one particular wavelength (e.g., blue light), so SSEs must be modified to generate white light. One conventional technique for modulating the light from SSEs includes depositing a converter material (e.g., phosphor) on the SSE. For example, FIG. 1A shows a conventional SSL 10 that includes a support 2, an SSE 4 attached to the support 2, and a converter material 6 on the SSE 4. The SSE 4 typically emits blue light that stimulates the converter material 6 to emit light at a desired frequency (e.g., yellow light). The combination of the emissions from the SSE 4 and the converter material 6 appears white to human eyes if the wavelengths of the emissions are matched appropriately.
FIG. 1B shows a conventional structure for the SSE 4 that includes a silicon substrate 12, an N-type gallium nitride (“GaN”) material 14, an indium gallium nitride (“InGaN”) material 16 and/or GaN multiple quantum wells, and a P-type GaN material 18 on one another in series. The SSE 4 shown in FIG. 1B can be a lateral-type device that includes a first contact 20 on the P-type GaN material 18 and a second contact 22 on the N-type GaN material 14 spaced laterally apart from the first contact 20.
On challenge associated with conventional SSLs (e.g., the SSL 10 shown in FIG. 1A) is that SSL packages generally only emit light from a single plane. For example, a conventional SSL can include a plurality of SSEs arranged in an array on one surface of a carrier substrate. The combination of conventional SSLs to multiple planes of a package can complicate manufacture and increase the vertical and lateral size of the package. However, devices having multi-plane light emission are desirable for many applications (e.g., light posts).
Another challenge associated with conventional SSLs is that some of the components are sensitive to heat. Although SSLs produce less heat than conventional lighting devices, the heat generated by the SSEs can cause such heat sensitive components to deteriorate and fail over time. For example, the phosphor and the junctions in the light producing materials deteriorate at a faster rate at higher temperatures than at lower temperatures. The deterioration of the phosphor causes the light to change color over time, and the deterioration of the junctions reduces the light output at a given current (i.e., reduces the efficiency) and the life span of the device. Adding SSEs to a SSL device increases the heat of the device and thus accelerates the deterioration of the heat sensitive components.